None.
Not applicable
1. Field of the Invention
The present invention relates generally to the field of processing a waste product and producing synthesis gas (xe2x80x9csyngasxe2x80x9d) and useable solid products. More particularly, this invention relates to a method and apparatus for processing a waste product, secondary material, or other feedstock containing carbon by employing a heated rotatable drum and a plasma reactor.
2. Background of the Invention
A gasification system is generally defined as an enclosed thermal device and associated gas cleaning system or systems that does not meet the definition of an incinerator or industrial furnace, well known to those skilled in the art, and that: (1) limits oxygen concentrations in the enclosed thermal device to prevent the full oxidization of thermally disassociated gaseous compounds; (2) utilizes a gas cleanup system or systems designed to remove contaminants from the partially oxidized gas that do not contribute to its fuel value; (3) transforms inorganic feed materials into a molten, glass-like substance (xe2x80x9cslagxe2x80x9d) at temperatures above 2000xc2x0 F.; and (4) produces a synthesis gas.
Utilizing a plasma arc to gasify a material is a technology that has been used commercially for many years. Most plasma arc reactors produce a high quality syngas that can be used as a building block for other chemical manufacturing processes or as a fuel for energy production. Many feeds containing hydrocarbons, such as oil, coal, refinery residuals, and sewage sludge have all been successfully used in gasification operations. It is sometimes desirable to convert a hazardous stream of material into a useable product by gasifying the material. Upon gasification, the hazardous material, or feed, will typically be converted into a useable syngas and a useful molten material, or a molten glass-like substance called slag or vitreous frit. Since the slag is in a fused, vitrified state, it is usually found to be non-hazardous and may be disposed of in a landfill as a non-hazardous material, or sold as an ore, road-bed, or other construction material. It is becoming less desirable to dispose of waste material by incineration or desorption because of the extreme waste of fuel in the heating process and the further waste of disposing, as a residual waste, material that can be converted into a useful syngas and solid material.
Generally, the gasification process consists of feeding carbon-containing materials into a heated chamber (the gasifier) along with a controlled and limited amount of oxygen and steam. At the high operating temperature created by conditions in the gasifier, chemical bonds are broken by thermal energy and by partial oxidation, and inorganic mineral matter is fused or vitrified to form a molten glass-like substance called slag or vitreous frit. With insufficient oxygen, oxidation is limited and the thermodynamics and chemical equilibrium of the system shift reactions and vapor species to a reduced, rather than an oxidized state. Consequently, the elements commonly found in fuels and other organic materials end up in the syngas.
However, the carbon-containing feed materials may be difficult to manage because they are typically in an improper form for gasification. Furthermore, syngas produced by a plasma reactor is usually very hot, dirty, and difficult to manage. Therefore the industry would welcome a gasification system which is self-regulating, self-cleaning, and which produces a higher quality syngas and/or useable solid by-product.
The present invention overcomes certain deficiencies of the prior art.
Disclosed is an apparatus and method for processing a waste stream wherein a heated, sealed rotatable drum preheats and prepares the waste stream for gasification within a plasma reactor. The synthesis gas (syngas) produced by the reactor is used to heat the rotatable drum and, consequently, cool the syngas. The syngas is a useable product and the molten metal, glass, and slag is useable or disposable as a non-hazardous material. The hot syngas may be blended with a colder gas and the blend used to preheat the feed. The hot syngas also may be conveyed through the inside of the rotating drum to cool and clean the gas, as well as to preheat the feed.
Another embodiment described herein includes a first plasma reactor to gasify the solid material in the feed, and a second plasma reactor to treat the untreated vapors, with the heat from the first reactor, or the second reactor, used to heat the rotating drum.